Pulse radar arrangement

ABSTRACT

A pulse radar system has a high-frequency source, which supplies a continuous high-frequency signal and is connected on the one side with a transmission-side pulse modulator and on the other side with two separately controllable pulse modulators in at least one receive path. Mixers are situated downstream from pulse modulators, respectively. The mixers evaluate a radar pulse reflected by an object together with the signal of the high-frequency source. The pulse radar system allows different modes of operation that may be changed in a simple manner.

FIELD OF THE INVENTION

The present invention is based on a pulse radar system, in particularfor close-range pulse radar applications in motor vehicles.

BACKGROUND INFORMATION

Radar sensors are used in automotive engineering for measuring thedistance to objects and/or the relative speed with respect to suchobjects outside of the motor vehicle. Examples of objects includepreceding or parked motor vehicles, pedestrians, bicyclists, or deviceswithin the vehicle's surroundings. The pulse radar functions, forexample, at 24,125 GHz and may be used for the following functions, stop& go, precrash, blind spot detection, parking assistant, and backup aid.

FIG. 1 shows a schematic representation of a radar device having acorrelation receiver of the related art. A pulse generation 302 causes atransmitter 300 to transmit a transmission signal 306 via an antenna304. Transmission signal 306 hits a target object 308 and is reflected.Received signal 310 is received by antenna 312. This antenna 312 may beidentical to antenna 304. After received signal 310 is received byantenna 312, the signal is transmitted to receiver 314 and subsequentlysupplied via a unit 316 having low pass and analog/digital conversion toa signal evaluation 318. The special feature of a correlation receiveris that receiver 314 receives a reference signal 320 from pulsegeneration 302. Received signals 310, which are received by receiver314, are mixed in receiver 314 with reference signal 320. As a result ofthe correlation, the time delay from the outside to reception of theradar impulses may be used as a basis for determining the distance of atarget object, for example.

A similar radar device is known from German Patent No. DE 199 26 787. Inthis context, a transmission switch is switched on and off by theimpulses of a generator so that a high-frequency wave generated by anoscillator and conducted via a fork to the transmission switch isswitched through to the transmission antenna during the pulse duration.A reception unit also receives the output signal of the generator. Thereceived signal, i.e., a radar pulse reflected by an object, is combinedwith the oscillator signal, which reaches the mixer via a receptionswitch, and evaluated during a predefined time period.

U.S. Pat. No. 6,067,040 also uses a transmission switch that is switchedon and off by generator impulses. Separate paths for l/Q signals areprovided for reception of the reflected radar pulses. Also in thisinstance, the received signal is only mixed and evaluated during apredefined time period.

SUMMARY OF THE INVENTION

The measures of the present invention enable the enhancement of theperformance of known pulse radar systems. In the case of the solutionaccording to U.S. Pat. No. 6,067,040, a reception-side pulse modulatoror pulse switch is positioned upstream from a power splitter forsplitting the LO (local oscillator) signal to the mixers in thereception-side IQ branches. This has the disadvantage that it is notpossible to realize a multi-receiver system or to simultaneouslyevaluate a plurality of different reception cells. However, in the caseof the solution of the present invention, two separately controllable,reception-side pulse modulators are provided via which the continuoussignal of the high-frequency source, which also controls thetransmission-side pulse modulator, may be switched to one respectivereception-side mixer. This means that in this instance, as opposed toU.S. Pat. No. 6,067,040, the signal of the high-frequency source may beapplied to every mixer in a reception branch at different instants, eachmixer also being able to be connected to the signal of thehigh-frequency source for different durations. In this manner, differentmodes of operation are made possible and may also be changed quickly andflexibly. Such a change may be effected simply by varying the delay timeof the time-delay circuits via which the reception-side pulse modulatorsmay be controlled. A plurality of operating modes may also runautomatically in a consecutive order according to a predefined scheme.

If both pulse modulators/switches are switched at the same time, thereceive path, which includes two reception branches of the pulse radarsystem, functions in the usual manner. If the switches are switched atdifferent times or they have opening times of different durations, allcapabilities of a multi-receiver system are available.

A plurality of settings or modes may be set. A previous detection rangeof, for example, 7 m may now be divided, e.g. into 0 to 4 m and 4 to 7m. An expansion of the detection range does not automatically result inan extension of the measurement times. One channel is able to cover the0 to 4 m range, while the other channel having a longer measurementtime, for example, covers the 7 to 14 m range. In special cases, theradar system of the present invention functions as a customary I/Qdemodulator. Furthermore, parallel to the distance measurement, achannel may be responsible for the CV (closing velocity) measurement,which may be used to determine radial velocity.

Therefore, in particular:

-   -   a plurality of receiving channels may be operated in parallel;    -   I/Q demodulator operation and individual operation are rendered        possible;    -   a plurality of antennas may be operated in parallel        (multi-receiver principle);    -   the pulse duty factor may be selected to be different in the        transmit and receive paths;    -   the pulse duty factor may be one (Doppler radar only);    -   the radar pulses may vary with respect to their repetition        frequency and/or pulse duration to increase the level of        interference protection;    -   a plurality of reception cells may be evaluated at the same time        when using double or triple transmission pulse power;    -   the power of the reception pulses may be split among a plurality        of receive paths in the case of target objects that are too        strong in close range so that overloading of subsequent        received-signal amplifiers is prevented;    -   a PN code may be provided with a reception sequence        corresponding to the set distance;    -   a cross echo analysis is possible;    -   the superimposition of two orthogonal codes in the transmit path        may be provided as well as evaluation of in each case only one        of the transmitted orthogonal codes per reception branch on the        reception side.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic representation of a radar device of the relatedart.

FIG. 2 shows a block diagram of a pulse radar system according to thepresent invention.

FIG. 3 shows a block diagram of a pulse radar system according to thepresent invention having common pulse processing.

FIG. 4 shows a block diagram of a pulse radar system according to thepresent invention having a plurality of receive paths.

DETAILED DESCRIPTION

The radar sensor of the present invention shown in FIG. 2 has ahigh-frequency source 1, which provides a continuous high-frequencysignal (CW signal). Via a signal splitter in the form of a splitconnection 2, this high-frequency signal reaches on the one side theinput of a transmission-side pulse modulator 3 for transmitting radarimpulses to transmission antenna 61 and on the other side via a furthersignal splitter 8 directly to the inputs of two reception-side pulsemodulators 71 and 72. The outputs of these pulse modulators 71 and 72are connected to a mixer 4 and 5, respectively. The outputs of thesemixers 4 and 5 are then connected via a power splitter 9, e.g. a 3 dBsignal splitter, to receiving antenna 6. Two reception branches areprovided with two pulse modulators 71, 72 and two mixers 4 and 5 inorder to achieve I/Q (inphase/quadrature phase) capability of the radarsystem. Signal splitter 9 is used for the reception-side splitting ofthe antenna signal into the quadrature component signals I and Q. Mixers4 and 5 are designed, for example, as balanced mixers in the form of aRAT-RACE hybrid (see in particular European Patent Application No. EP685 9 30, which describes the system of such a RAT-RACE hybrid). Thecontinuous signal of high-frequency source 1 may be switched via pulsemodulators 71 and 72 in each case to one of mixers 4 and 5.Transmission-side pulse modulator/switch 3 is controlled via a pulsesignal source 10 and a transmission gate circuit 101. Pulse modulators71 and 72 are each controlled separately by pulse signal sources 11 and12, to which a time-delay circuit 21 and 22 as well as a reception gatecircuit 211 and 212 are respectively assigned.

If a radar pulse reflected by an object travels from antenna 6 acrosspower splitter 9 to mixers 4 or 5, the envelope curve of the receivedpulse (IF signal) is formed from the continuous signal of thehigh-frequency source and the reflected radar pulse during the time inwhich the pulse modulator allows the signal of high-frequency source 1to pass. This mixed signal/envelope curve is amplified by an IFamplifier 411 or 412 with a bandwidth of, e.g. 10 kHz, and supplied to areception scanner 413 or 414. This occurs separately for the I and the Qchannel (separate receive and evaluation paths for the received I and Qsignal).

Time-delay circuits 21 and 22 are necessary to be able to compare theduration of the received radar pulse and to obtain distance informationtherefrom. After a defined time period following the generation of thetransmission pulse that corresponds with the pulse duration for thedesired distance cell, a particularly short scanning pulse is applied toa broadband scanner 413 and 414, respectively, and the scanner scans theoutput signal of IF amplifier 411 and 412, respectively, in the selecteddistance cell. In this context, the duration of the scanning pulse is inthe order of magnitude of the transmission and IF pulse width. Thisoccurs at the rate of transmission pulse generation, but accordinglydelayed. The variation in delay time allows the scanning of the desireddistance range in the same manner as SRR (short range radar). Thescanner detects from 0 different voltages and thus detects the pulsereturn after the desired duration. Incoherent pulse integration ispossible and is improved by the signal to noise ratio proportionally toSQRT (n), n being the number of integrated pulses.

According to FIG. 3, the control pulses for pulse modulators 3, 71, 72may also be jointly processed by a shared pulse signal source 100. Sincethe delay times of time-delay circuits 21 and 22 may be selected to bedifferent, pulse modulators 71 and 72 may be controlled independently ofone another also in this instance. Of course, in an alternative, onlytransmission-side pulse modulator 3 may have its own pulse signal source10, a common pulse signal source then being provided for thereception-side pulse modulators.

FIG. 4 shows an exemplary embodiment having a plurality of receivepaths, two in this instance. The individual receive paths may beconfigured as shown in FIG. 2 or 3. As in FIGS. 2 and 3, every mixer 4,5 and 41, 51, respectively, has a separate pulse modulator 71, 72 and711, 721, respectively, which may be controlled independently of therespective other mixers of the same receive path via a correspondingpulse signal source 11, 12 and 111, 121, respectively, time-delaycircuit 21, 22 and 211, 221, respectively, and reception gate 212, 213and 214, 215, respectively. The individual receive paths may have eithera common receiving antenna or each have a separate receiving antenna 62,63. Additional downstream signal splitters 91, 92 are required toconnect mixers 41, 51 of the further receive paths to high-frequencysource 1, which is shared by all receive paths.

As a result of the at least two receive paths and separate control ofreception-side pulse modulators 71, 72 and 711, 712, respectively, eachhaving adjustable time-delay circuits 21, 22, 211, 221 at differentdelay times, different modes of operation are possible as well as afaster change between these different modes of operation as a functionof the needs of the vehicle operator. As a result, in particular:

-   -   a plurality of channels (mixers) may be operated in parallel;    -   a plurality of antennas may be operated in parallel        (multi-receiver principle);    -   the pulse duty factor may be selected to be different in the        transmission and receive paths;    -   the pulse duty factor may be one (Doppler radar only);    -   the transmission pulses may vary with respect to their        repetition frequency and/or pulse duration in particular to        increase the level of interference protection;    -   I/Q demodulator operation and individual channel operation are        possible;    -   a plurality of reception cells may be evaluated at the same time        with the same degree of sensitivity when using double or triple        transmission pulse power;    -   the distance cells may be adjusted by scanning or masking the        received signal;    -   the reception pulse power may be split in the case of target        objects that are too strong in close range so that in particular        overloading of subsequent amplifiers is prevented;    -   a cross echo analysis is possible;

If coded sequences of pulses (PN coding) are transmitted, the modulatorsin the receive paths, e.g. phase rotators in this case, are controlledby a reception sequence corresponding with the set distance. Thiscontributes significantly to the suppression of false targets. Thechannels monitor different distance ranges. In the event that areception-side device is set to the PN code of a neighboring device, across echo analysis is possible.

Superimposition of two orthogonal codes may be provided in the transmitpath, and in each case only one of the transmitted orthogonal codes isevaluated per receive path.

The transmission-side and reception-side pulse signal sources 10, 100,11, 12, 111, 121 are phase-coupled to one another, or only thereception-side pulse signal sources 11, 12, 111, 121 are phase-coupledamong one another, particularly in the case of a plurality of receivepaths, in order to achieve defined time relationships particularly forthe simultaneous monitoring of a plurality of reception cells.

In the present invention, a plurality of operating modes may be setconsecutively according to a predefined scheme. For this purpose, only ashared control switch 400 is needed for the pulse signal sources and/orthe time-delay circuits that provide in each case the time window fortransmission and evaluation of the radar pulses according to thepredefined scheme. The different parameters for the individual modes ofoperation may be loaded in a memory module provided in the controlcircuit or supplied by a separate memory module 401. Of course, thecontrol of the modes of operation may also be configured to beinteractive, i.e., modified parameters may be provided in a first modeof operation for further modes of operation as a function of theevaluation.

1-15. (Canceled).
 16. A pulse radar system comprising: a high-frequencysource for emitting a continuous high-frequency signal; atransmission-side pulse modulator coupled on a first side of thehigh-frequency source for emitting radar pulses; at least tworeception-side mixers; and at least two separately controllablereception-side pulse modulators coupled on a second side of thehigh-frequency source in reception branches, the at least two pulsemodulators being adapted to switch the continuous signal of thehigh-frequency source in each case to one of the at least tworeception-side mixers.
 17. The pulse radar system according to claim 16,wherein the system is for a close-range pulse radar application for amotor vehicle.
 18. The pulse radar system according to claim 16, furthercomprising two pulse signal sources, each of which including a separatetime-delay circuit, the two pulse signal sources being for controllingthe reception-side pulse modulators.
 19. The pulse radar systemaccording to claim 16, further comprising a shared pulse signal sourcefor controlling the reception-side pulse modulators, the shared pulsesignal source being connected with each of separate time-delay circuitsfor each one of the reception-side pulse modulators.
 20. The pulse radarsystem according to claim 19, wherein the shared pulse signal sourcealso provides a pulse signal for the transmission-side pulse modulator.21. The pulse radar system according to claim 16, further comprising aquadrature power splitter situated between a receiving antenna and thereception-side mixers, so that an in-phase received signal is suppliedto one of the mixers and a quadrature received signal is supplied toanother of the mixers.
 22. The pulse radar system according to claim 16,further comprising a signal splitter device for splitting a continuoussignal of the high-frequency source to the transmission-side pulsemodulator and to the reception-side pulse modulators.
 23. The pulseradar system according to claim 16, further comprising a separate pulsesignal source for the transmission-side pulse modulator.
 24. The pulseradar system according to claim 16, further comprising at least onefurther receive path with corresponding receiving antennas,reception-side mixers, reception-side pulse modulators, further signalsplitters and pulse signal sources.
 25. The pulse radar system accordingto claim 24, wherein the reception-side pulse modulators of the at leastone further receive path are connected via the further signal splitters,which are downstream from the high-frequency source.
 26. The pulse radarsystem according to claim 24, further comprising a plurality of receivepaths and a plurality of evaluation devices for evaluating a pluralityof distance cells at the same time.
 27. The pulse radar system accordingto claim 16, further comprising transmission-side and reception-sidepulse signal sources phase-coupled to one another.
 28. The pulse radarsystem according to claim 16, further comprising transmission-side andreception-side pulse signal sources, the reception-side pulse signalsources being phase-coupled among one another, and further comprising aplurality of receive paths.
 29. The pulse radar system according toclaim 16, wherein pulse duty factors of radar pulses in a transmit pathand at least one receive path are different.
 30. The pulse radar systemaccording to claim 16, wherein radar pulses are PN coded, and thereception-side pulse modulators are controlled using a receptionsequence corresponding to a set distance.
 31. The pulse radar systemaccording to claim 16, wherein a cross echo analysis is provided, suchthat, with a plurality of receive paths, a reception-side device is setto a PN code of a neighboring device.
 32. The pulse radar systemaccording to claim 16, wherein a superimposition of two orthogonal codesis provided in a transmit path, and a reception branch/path evaluates ineach case only one of transmitted orthogonal signals.